Reaction Steps
Compound 2 of Example 2 (10.85 g) was dissolved in dry dimethylformamide (DMF, 120 mL) containing imidazole (1.63 g) and 4 Å molecular sieves and cooled in an ice bath. To this, t-butyldimethylsilyl chloride (tBDMS chloride, 3.6 g) was added and stirred at this temperature for 10 min and then at room temperature 1 h. Another portion of imidazole (1.05 g) and tBDMS chloride (2.34 g) were added to the ice cold solution and stirred for 1 h. Methanol (1 mL) was added and the reaction mixture was evaporated to dryness. The residue was dissolved in CH2Cl2 and washed with water, 1M ice cold HCl and saturated NaHCO3 solution. The solution was dried over anhydrous magnesium sulfate, filtered and evaporated. 1H n.m.r. of the crude product (12.0 g of colorless solid) showed it to be essentially pure titled compound. [α]D25 -3.2±2° (c 1.03, CHCl3). 1H n.m.r.(CDCl3 +D2O<5 %) ∂: 5.95 (m, 1 H, --CH=C), 5.33 and 5.23 (m, 2 H, C=CH2), 4.24 (m, 3 H, H-1, J1,2 =Hz, O--CH2 --C=), 4.06 (d, H-4), 3.9-3.8 (m, 3 H, H-6a,b, OCH2 --C), 3.73 (dd, H-2), 3.67 (s, COOCH3), 3.52 (m, OCH2 --C), 3.44 (m, H-5), 3.35 (dd, H-3),2.32 (t, CH2COO), 1.65 and 1.40 (6 H, hydrogens of pentyl group), 0.89 (s, t-butyl group), 0.09 (d, CH3 --Si--CH3). 13C n.m.r. (CDCl3) ∂: 173.9, 134.8, 117.4, 103.2, 80.7, 75.0, 71.2, 71.0, 69.3, 66.3, 62.2, 51.3, 33.9, 29.2, 25.9, 25.6, 24.6, 18.3, -5.34, -5.39. Anal. Calcd for C22H2842O8Si: C, 57.14; H, 9.09. Found: C, 56.30; H 9.06.
